Compression test help..

[smartass12]

Just bough a 2002 5.3...doing a compression test with results that are freaking me out...hope im doing it wrong...only have done them on sbc figured was the same..here are the variables..

all plugs out, throttle body valve open, cycling starter through 4-5 complete strokes (more doesnt seem to raise it) ive got 45 psi in the cylinders, 60psi in three more, 10psi in one and 80psi in the other...i know there is some oil in motor but not sure how much because the dip stick is missing (not sure if that matters) also i dont have any of the harness hooked up buy dont think that matters either..

Can some one please chime in and tell me im a dumb a@# and doing it wrong?

[clinebarger]

Compression test are almost worthless on a engine that's been sitting.
I use a leak-down tester.

[smartass12]

Originally Posted by clinebarger

Compression test are almost worthless on a engine that's been sitting.
I use a leak-down tester.

I that possibly why now (after trying a couple times per cylinder) im getting 70-85psi across the board now? Dont own a leak down tester but guess its time to buy one.

[smartass12]

So here are the results of the leakdown test (im pretty sure i did it right)

Cylinder Leak down % Where i mainly hear the leak

1 15% exahust
2 5% oil filler
3 5% oil filler
4 8% oil filler
5 8% oil filler
6 8% throttle body
7 10% oil filler
8 (kept pushing the piston down under pressure/didnt get test)


With that being said,,,what do you guys think? did i buy a blown motor? Could 1 be so much higher because it has sat and might have a stuck valve??

[clinebarger]

Im concerned about #1.....15% is on the high side, & air coming out the exhaust isnt good.

But not all is lost.....

Pull the schrader valve out of the "compression test whip" you were using.
Install the whip in Cyl. #1.
Connect your air hose straight to the whip.
The piston will bottem in the bore.
You will now hear the air leak out of the exhaust valve.
Using a rubber mallet, Squarely hit the top of the exhaust valve/spring.
This will "pop" the valve open & let high pressure air past....If a peice of carbon or something is stuck between the seat & valve....The air may push it out.
If the air noise stops, Repeat the leakdown test.
If you cant get the leak stopped.....Time for a valve job.

[JGross]

I just did a compression test on a junkyard 5.3 that i got for putting in my 65 C10. I conducted the test the same way you did and i got 170 to 180 psi in all cyclinders. Could your test gauge be bad?
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[smartass12]

Originally Posted by clinebarger

Im concerned about #1.....15% is on the high side, & air coming out the exhaust isnt good.

But not all is lost.....

Pull the schrader valve out of the "compression test whip" you were using.
Install the whip in Cyl. #1.
Connect your air hose straight to the whip.
The piston will bottem in the bore.
You will now hear the air leak out of the exhaust valve.
Using a rubber mallet, Squarely hit the top of the exhaust valve/spring.
This will "pop" the valve open & let high pressure air past....If a peice of carbon or something is stuck between the seat & valve....The air may push it out.
If the air noise stops, Repeat the leakdown test.
If you cant get the leak stopped.....Time for a valve job.

Thank you for that info I will get started on that tomorrow and see how it goes, I am I okay on the others I know it's not great but is it doable?

Originally Posted by JGross

I just did a compression test on a junkyard 5.3 that i got for putting in my 65 C10. I conducted the test the same way you did and i got 170 to 180 psi in all cyclinders. Could your test gauge be bad?
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It could be I only paid 40 dollars for it so I assume it's not a really high precision gauge
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[paul mora]

This is Paul for a guy who says he needs alot of help you seem to be doing pretty good I courious what part of OC do you live in?
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[smartass12]

Originally Posted by paul mora

This is Paul for a guy who says he needs alot of help you seem to be doing pretty good I courious what part of OC do you live in?
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Hey paul, thanks again for the painless....i live in missiln viejo/rsm
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